Intersomatic cage with unified grafts

ABSTRACT

An intervertebral cage includes a thin main wall having two return parts at opposite ends of the wall. The wall has an approximately constant thickness. The return parts are extended by facing end parts having a gap between them. The wall, the return parts and end parts delimit an inner cavity. The gap extends parallel to the wall and has a length between 50% and 100% of the cavity length. The gap length is preferably between 70% to 90% of the cavity length.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/767,386 filed Jun. 22, 2007, now U.S. Pat. No. 8,623,087issued Jan. 7, 2014, which is a continuation of U.S. patent applicationSer. No. 10/276,712 filed Mar. 26, 2003, now U.S. Pat. No. 7,291,170issued Nov. 6, 2007, which is a 35 U.S.C. §371 application ofPCT/FR01/01545 filed May 18, 2001, which claims priority to FR 00/06351filed May 18, 2000. All of the foregoing are hereby incorporated byreference.

FIELD OF INVENTION

The present invention relates to an intervertebral cage designed to beplaced between two vertebrae to restore and/or maintain theintervertebral space, to replace the intervertebral disk. After the cageor implant has been placed, the intervertebral space is filled withautologous spongy bone or adapted bone substitutes. This invention alsorelates to instrumentation for placement of the intervertebral cage.Finally, it also relates to a pair of intervertebral cages of this type.

BACKGROUND ART

Prior art has already described intervertebral cages, for exampleStryker cages. These cages are parallelepiped-shaped, the bottom and thetop of the cage being completely open, the side and top openings will beplaced facing the two vertebrae that are to be kept at a distance fromeach other. Spongy bone is then compacted inside the cage to finallycause fusion of the bone (or arthrodesis) of the two vertebrae separatedby a suitable disk space.

For posterior placement, there are usually two cages adjacent to eachother at a distance from each other in the intervertebral space, and thegraft is firstly compacted inside the two cages and secondly the spacebetween the two cages is filled in by spongy bone or bone substitute.

It is found that the growths of the three independent grafts (two insidethe cages and one between the cages) vary with respect to each other. Inparticular, the graft placed between the cages contributes more quicklyto the fusion than the compacted grafts inside the cages. Obviously,this is a disadvantage, particularly with regard to the stability of thegrafts and the two vertebrae held in place by these grafts, andconcerning the time necessary to obtain good stability.

Document WO/98/55052 also discloses intervertebral cages.

In the first case, they are composed of a main very thick curved partparticularly with a thickness that increases from the middle towards theends. Therefore, these cages are complicated to make due to their curvedshape.

In the second case, they are composed of a straight main part and returnparts each being prolonged by an end part that together form a smallinterval less than 25% of the longitudinal extension of the internalhousing of the cage.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages mentioned above byproposing an intervertebral cage that enables good growth of the graftor grafts placed between the vertebrae and is each to make, particularlydue to the fact that it has straight longitudinal walls, and has goodresistance to compression forces applied by the vertebral plates,particularly in the case of posterior implantation in which twointervertebral cages are placed side by side at a distance from eachother.

According to the invention, the intervertebral cage is composed of athin main wall prolonged by two return parts, the thin main wall havingan approximately constant thickness and each return part being extendedby an end part, the end parts facing each other with a gap between them,the wall, the return parts and the end part delimiting an inner cavity,the extension of the clear gap parallel to the straight wall beingbetween 50% and 100% of the largest dimension of the cavity parallel tothe wall, and preferably between 70% and 90%.

Thus, according to the invention, the intervertebral cage comprises onlythree walls, namely the straight main wall and the two return partsprolonged by the end parts, such that the graft that was compacted onthe inside of each cage before the cage was placed (in the case ofposterior placement in which two cages are used arranged side by sideand at a spacing from each other), and the graft that is made to growbetween the two cages are all three in mutual contact, such that thereis actually only a single graft which will therefore grow homogeneouslyto obtain an optimum contact between the vertebral plate-graft-vertebralplate, in other words a good homogeneous and stable contact, also makingthe cage more resistant even though it only has one straight main walland a large gap between the end parts.

The applicant realized before anyone else that in the case in whichthere is a main part in the form of a straight wall, it is stillpossible to significantly move the end parts away from the return partswithout endangering the stability and the strength of the intervertebralcages between the vertebral plates. The applicant believes that the factthat the central graft and the compacted grafts in the internal parts ofthe two cages arranged with their openings facing each other fusetogether well and helps to make the two cages more resistant to thetension forces exerted by the vertebral plates, and it is thereforepossible to increase the air gap between the end parts, although themain part is only a thin single straight wall; but this is only ahypothesis that the applicant cannot confirm.

According to one preferred embodiment of the invention, the thin mainwall is a straight wall.

According to one advantageous embodiment, the thickness of the end partsis the same as the thickness of the thin main wall.

According to one advantageous embodiment, the thickness of the thin mainwall is between 1 mm and 5 mm and preferably between 2 mm and 4 mm, forexample 3 mm.

According to one advantageous embodiment, the end part that projectsfrom the largest return part is provided with at least one hole, andpreferably two holes on the front face facing the other end part, andthe other return part comprises a threaded hole on its part external tothe cage, these holes being designed to cooperate with pins associatedwith placement instrumentation for placement of the implant or theintervertebral cage in the intervertebral space.

The present invention also relates to instrumentation for placement ofan intervertebral cage, particularly by posterior placement.

According to the invention, the instrumentation for placement of anintervertebral cage between two vertebrae in the disk space comprises arod that will cooperate with associated coupling means formed in anouter surface of the intervertebral cage.

According to one improvement of the invention, the instrumentationcomprises a prolonged part in the form of a rectangular or slightlycurved wall, on the distal end of the rod, the dimensions and positionof which are such that the wall closes off the clear gap between the twoend parts, when the rod is in a position to cooperate with the couplingmeans.

The rectangular wall replaces the “missing wall” of the cage duringplacement, firstly to retain the graft that was compacted inside thecage before the cage was put into position, and secondly to make theassembly stiffer to facilitate its placement in the intervertebralspace.

For example, coupling means are composed of a hole formed in the outersurface of the cage, the hole being sized such that the rod can beinserted inside it.

According to the invention, it is also possible to use blocking meansthat will block mutual rotation of the cage and the instrumentation inthe position in which the rod and the coupling means cooperate with eachother.

For example, these blocking means may be composed such that the shape ofthe periphery of the hole is made hexagonal or to have at least oneflat, and one end of the rod has a matching shape.

According to one improvement of the invention, attachment means designedto fix the rod to the coupling means may also be provided. Theseattachment means, which in particular can be released, are used toinsert the cage such that it cannot accidentally stop cooperating withthe rod.

For example, these attachment means may consist of tapping the hole andproviding an associated thread at the distal end of the rod. In thiscase, the tapping in the hole and the thread on the rod also formblocking means.

According to one improvement to the invention, the outside distal edgeof the wall comprises two pins that can penetrate into the holes formedin the face on the end part of the cage.

According to the invention, the wall is offset with respect to thecentre line of the main rod, particularly by a distance equivalent tohalf of the dimension of the return part at the rod end.

The invention also relates to a pair of intervertebral cages accordingto the invention, in particular the two intervertebral cages of the pairbeing symmetric with each other like in a mirror.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The drawings, given solely as examples of one embodiment of anintervertebral cage according to the invention and instrumentation usedfor placement in the intervertebral space, are described.

In the drawings:

FIG. 1 is a perspective view of an intervertebral cage according to theinvention;

FIG. 2 is a view from the top of the intervertebral cage of FIG. 1;

FIG. 3 is a side view of the intervertebral cage in FIG. 1;

FIG. 4 shows instrumentation for placement of an intervertebral cageaccording to the invention, and also shows the intervertebral cage shownin FIG. 1;

FIG. 5 is an enlarged view of part of FIG. 4;

FIG. 6 is a perspective view of the enlarged part of the instrumentationof FIG. 4, without showing the intervertebral cage of FIG. 1;

FIG. 7 is a perspective view of the intervertebral cage of FIG. 1showing an attachment structure; and

FIG. 8 is a perspective view of the intervertebral cage of FIG. 1showing a blocking structure.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

FIG. 1 shows in intervertebral cage 1 according to the invention. Theintervertebral cage comprises a main wall 2 from which two return parts3 and 4 project. The two return parts 3 and 4 are prolonged by a firstend part 5 and a second end part 6 respectively. The two end parts 5 and6 are approximately parallel to the main wall 2. The wall 2, the returnparts 3 and 4 and the end parts 5, 6 delimit an inner cavity 30 in thecage, by prolonging the two end parts towards each other.

The two end parts 5, 6, are at a distance from each other and there is aclear gap between them. The clear gap extends along the direction of thelength parallel to the main wall 2 over a length equal to 78% of thelongest length of the inner cavity 30.

The two end parts 5, 6 face each other through a first end face 7 and asecond end face 8. The main wall 2 is 3 mm thick. The thickness of theend walls is the same as the thickness of the main wall 2. The tworeturn parts 3 and 4 are approximately perpendicular to the main wall 2.The two end parts 5 and 6 extend from the return parts 3 and 4 that areapproximately perpendicular to the end parts, parallel to the main wall2, such that the shape of the cage 1 forming the intervertebral cage isapproximately like a C with a straight back in the cross-sectional plane(see FIG. 2).

The upper edge 9 and the lower edge 10 of the cage forming theintervertebral cage have a toothed shape 11. These teeth or notches givegood anchorage of the cage in the vertebral plates.

Two holes 12 are formed in face 8, facing the end part 5. A tapped hole13 is formed in the outside edge of the return part 4. These holes 12and 13 are designed to cooperate, respectively, with the pins 20 and thethreaded end 21 of the rod 15 of an instrument 14 for the placement ofan intervertebral cage between the two vertebrae, particularly byposterior placement. In particular, this instrumentation 14 is shown inFIGS. 4 to 6.

It comprises a hollow rod 15 that is extended at its end 16 by a part 17in the form of a wedge comprising a surface 18 perpendicular to thecentre line of the rod 15 and a wall 19 forming an angle of about 75°from the surface 18. The shape of the wall 19 is rectangular. The anglebetween the wall 19 and the surface 18 depends on the extended length ofthe clear gap. It is designed such that the wall 19 completely fills theopening between the two end parts 5 and 6.

On its edge opposite the rod 15, the plate or wall 19 comprises two pins20 designed to cooperate with holes formed in the face 8 of theintervertebral cage 1. The instrumentation 14 also comprises a threadedend 21 (FIG. 6) of the rod 15 that will cooperate with the tapped hole13 (FIG. 7) formed in the outside part of the return part 4 of theintervertebral cage. This threaded end 21 extends inside the rod 15 andopens up at the end of 16 of this rod 15, at the surface 18 through ahole formed in it. The user screws and unscrews the threaded rod usingthe maneuvering handle 22. Screwing the rod in firstly blocks the rodand the cage in rotation, and secondly fixes the rod to the cage.

The length of the plate 29 is approximately equivalent to the length ofthe main wall 2 of the intervertebral case, such that when the threadedend 21 is screwed into the tapped hole 13, pins 20 (FIG. 7) penetrateinto the holes 12. It is thus possible to insert the intervertebral cagebetween two vertebrae and then to remove the instrumentation. The twosides 7 and 8 facing the end parts 5 and 6 are offset from each other bya dimension corresponding to the thickness of the plate 19.

The wall 19 replaces the “missing wall” of the cage during placement,firstly to fix the position of the graft that was compacted in the cagebefore its placement, and secondly to make the assembly stiffer tofacilitate its placement in the intervertebral space.

Finally, the cage may be bevelled in the longitudinal direction (seeFIG. 3). This bevelled shape makes it possible to restore the lordosis.

The invention claimed is:
 1. An intervertebral cage configured forinsertion between an upper vertebra and a lower vertebra, comprising: anelongated main wall having first and second opposing ends thereof; afirst return part extending away from the first end of the main wall; asecond return part extending away from the second end of the main wall;a first end part extending from the first return part and terminating ata first end face; a second end part extending from the second returnpart and terminating at a second end face; a substantially planar uppersurface configured for contact with the upper vertebra, the uppersurface comprising teeth and at least portions of the main wall, thefirst return part, the second return part, the first end part, and thesecond end part; a substantially planar lower surface configured forcontact with the lower vertebra, the lower surface comprising teeth andat least portions of the main wall, the first return part, the secondreturn part, the first end part, and the second end part; a cavitydelimited by the main wall, the first return part, the second returnpart, the first end part, and the second end part, with the cavity openalong the upper surface and the lower surface and with the first returnpart and the second return part separated across the cavity by a firstdistance; and a gap formed between the first end face and the second endface, the gap open at the upper surface and the lower surface andextending therebetween so that the first end part and the second endpart are connected only through the first return part, the second returnpart, and the main wall, with the intervertebral cage opened to thecavity along the gap such that the first end face and the second endface are separated by a second distance that is less than the firstdistance.
 2. The intervertebral cage of claim 1 in which the main wallis substantially straight.
 3. The intervertebral cage of claim 2 inwhich the main wall has a substantially constant thickness between theupper and lower surface.
 4. The intervertebral cage of claim 3 in whichthe main wall and the first and second end parts have substantially thesame thickness.
 5. The intervertebral cage of claim 1 in which the firstend face and the second end face are substantially flat andsubstantially parallel.
 6. The intervertebral cage of claim 1 whereinthe gap extends substantially parallel to the main wall and correspondsto between 100% and about 50% of the largest dimension of the cavityparallel to the main wall.
 7. The intervertebral cage of claim 1 whereinthe gap extends substantially parallel to the main wall and correspondsto between about 90% and about 70% of the largest dimension of thecavity parallel to the main wall.
 8. The intervertebral cage of claim 1further comprising a longitudinal bevel adapted to restore a lordosis.9. The intervertebral cage of claim 1 in which the teeth of the uppersurface and the lower surface each extend along the main wall, the firstreturn part, the second return part, the first end part, and the secondend part.
 10. The intervertebral cage of claim 1 further comprising acoupler for a placement instrument adapted to place the cage between theupper and lower vertebrae.
 11. The intervertebral cage of claim 10further comprising an instrument for inserting the cage between theupper and lower vertebrae, the instrument comprising a rod attachable tothe coupler and an instrument wall adapted to extend at least partiallyinto the gap and to close the gap between the first and second endfaces.
 12. The intervertebral cage and instrument of claim 11 whereinthe instrument wall is offset from a center line of the rod.
 13. Theintervertebral cage and instrument of claim 11 further comprising ablocking structure adapted to block rotation of the cage.
 14. Theintervertebral cage and instrument of claim 13 wherein the blockingstructure comprises at least one flat part matching a flat part at theend of the rod.
 15. The intervertebral cage and instrument of claim 14wherein the blocking structure comprises matching hexagonal peripheries.16. The intervertebral cage and instrument of claim 11 wherein thecoupler includes a hole disposed in the cage adapted to receive aportion of the rod.
 17. The intervertebral cage and instrument of claim16 further comprising a blocking structure integral with the coupler,wherein the hole disposed in the cage is tapped and the portion of therod received in the hole is threaded.
 18. An intervertebral cageconfigured for insertion between an upper vertebra and a lower vertebra,comprising: a main wall comprising a top adapted for contact with theupper vertebra and a bottom adapted for contact with the lower vertebra,the main wall having a substantially constant thickness between the topand the bottom and having first and second ends each extending from thetop to the bottom of the main wall; a first return part extending awayfrom the first end of the main wall, the first return part having a topadapted for contact with the upper vertebra, a bottom adapted forcontact with the lower vertebra, and a first end part having a topadapted for contact with the upper vertebra and a bottom adapted forcontact with the lower vertebra; a second return part extending awayfrom the second end of the main wall, the second return part having atop adapted for contact with the upper vertebra, a bottom adapted forcontact with the lower vertebra, and a second end part having a topadapted for contact with the upper vertebra and a bottom adapted forcontact with the lower vertebra, the first end part extending from thefirst return part toward the second end part and the second end partextending from the second return part toward the first end part so thatthe first and second end parts face each other to form a gaptherebetween; and a cavity defined by the main wall, the first andsecond return parts and the first and second end parts that opens fromthe cage at the gap, the gap extending substantially parallel to themain wall a distance that is less than 100% but greater than about 50%of a largest dimension of the cavity parallel to the wall.
 19. Anintervertebral cage configured for insertion in a space between an uppervertebra and a lower vertebra, the intervertebral space having a medialhorizontal plane, the cage comprising: a substantially straight mainwall having two ends; first and second return parts each projecting fromone of the two main wall ends; a first end part extending toward thesecond return part from an end of the first return part distal from themain wall; a second end part extending toward the first return part froman end of the second return part distal from the main wall; a gapbetween the first and second end parts; an inner cavity defined by themain wall, the first and second return parts, the first and second endparts, and the gap, with the gap extending substantially parallel to themain wall along a distance that is less than 100% but greater than about50% of the largest dimension of the inner cavity parallel to the mainwall; a substantially planar notched top surface adapted to confront theupper vertebra; a substantially planar notched bottom surface adapted toconfront the lower vertebra; and a cross-sectional shape along the topand the bottom surfaces of the cage that approximates the shape of aletter “C” having a substantially straight back.
 20. The intervertebralcage of claim 19 in which the cage has a lateral width and the notchesof the top and bottom surfaces each extend across the lateral width.